The present invention relates to trim strips or molding and, more particularly, to a trim strip or molding manufactured from a combination of injection molding and extruding processes.
In commonly known injection molding operations, generally the molds utilized in the operation are very heavy, sturdy and durable. This is due to the fact that the material injected into the molds is at elevated temperature and pressure. Thus, the molds must be very strong and durable to endure the increased temperature and pressure which also explains their high cost.
During the manufacturing of trim strips with metal cores, which are formed from a metal forming process, the passed strips may include what is known in the field as "surface chatter". Surface chatter is the irregular appearance of the outer plastic layer caused by vibration of the metallic core as it passes through the metallic extruding dies. Surface chatter detracts from the appearance and may render the trim strips useless causing the trim strips to be scrapped.
Another problem existing in the current injection process is molding an end cap onto the extruded strip. Generally if metallic colors are used in the strip, metallic "flow lines" will appear on the surface of the end caps. These flow lines present an objectionable appearance and sometimes cause the molded assemblies to be re-worked, by re-molding the end cap, or scrapped.
Another problem with the current injection process is that it requires two separate color compounds. One extrusion grade color and one injection molding grade color. Sometimes there are slight color mismatches that occur between these two color compounds. The color mismatch causes the parts to be re-worked, by re-molding the end cap, or scrapped if the extrusion color and injection color are off.
Another problem with the current injection process is molding an end cap to a co-extrusion. With an extrusion having a metal core with a shape that is entirely covered or in part covered by extruded material, the problem is that the end cap and the co-extrusion do not strongly bond between one another. If the bond is not of sufficient strength, the end cap will split away from the extrusion causing the part to be re-worked or ultimately scrapped.
Also, during manufacturing of trim strips utilizing an injection molding process for end caps, if there is a slight variation in the extrusion size, flash will appear on the edges of the molded end caps. The flash must be trimmed from the strip which requires additional time and labor to bring the trim strip within desired size and appearance specifications.
Another problem associated with trim strips which have been extruded or injection molded with a metallic color is known as metallic flop. Metallic flop is a phenomena which occurs during the extrusion or injection molding process which provides the trim strip with unidirectional characteristics. That is, the trim strip may only be positioned onto a surface in one direction to provide desired color characteristics. If the trim strip is applied to the vehicle in a reverse direction, the color characteristics of the material are different, e.g., the color of the strip does not match the color of the surface, indicating that the material has been flopped. Particularly, if two parts are laid side by side in the same orientation which they came out of a mold or extruder, that is their forward ends are positioned side by side and their rearward ends are positioned side by side, there would be no apparent difference in color between the two. However, if one of the strips were to be flipped such that the rearward end of one strip was positioned side by side the forward end of the other strip there would be a noticeable difference in color between the two parts. This is known as metallic flop. To alleviate the metallic flop problem, the trim strips are marked as they leave the factory to indicate which direction they should be applied onto the surface.
Another problem existing in current trim strip manufacturing is that with respect to coloring the trim strip. Since the color formulation of the plastic to manufacture the trim strip is ordinarily color checked in small quantities in a research laboratory by a researcher utilizing different apparatus than is utilized in the production of the trim strips, there sometimes is a difference in color. This coloring difference is generally due to the fact that the apparatus or machinery used to produce the color of the plastic of the trim strip in the laboratory is different than the machinery utilized for mass production of trim strips. Thus, once production trim strips are manufactured, if the color does not match the vehicle color, the color formulation of the trim strip must be modified so that the production machinery will produce the desired color appearance.
Trim strips made with current injection molding processes, with hollowed out portions on the underside that are irregular in position, are difficult to make. "Sinks" appear on the top finished surface in the areas where the cross section thickness undergoes a considerable change. These "sinks" degrade the appearance of the finished part surface.
Thus, it is desirous to have trim strips and a method of manufacturing trim strips which overcome the above disadvantages. Accordingly, the present invention provides the art with a trim strip which overcomes the above disadvantages.
The present invention provides the art with a trim strip which is manufactured by a molding process. The molding occurs at very low pressure, if any, to enable utilization of low cost lightweight molds. The trim strip or molding is formed by dispensing liquid plastic into a mold and applying heat to solidify the plastic. Also, a core, preferably an elongated metallic member, is added to the mold prior to the heating cycle. The core, which may have end stops, is adhered to the plastic material to form a one piece trim strip. Plastics that can be used in this invention may be liquid vinyls such as plastisols. The present invention, which is molded at very low pressure, produces trim strips which are substantially color non-directional and substantially eliminate metallic flop.
Since the metal core of the present invention is not passed through extruding dies, the vibration is eliminated and surface chatter is likewise eliminated. Also, due to the flow and molding characteristics of the liquid plastic, the chance of metallic flow lines is substantially eliminated. Further, flash trimming is eliminated because the plastic surface is a "one-piece" construction without joint lines from the end caps.
Also, on account of the low pressure, trim strips with large abrupt changes in thickness may be manufactured without "sinks" on the finished surface. This characteristic is becoming more important due to the trend of new designs requiring high gloss smooth surfaces on new automotive applications where sinks are more noticeable.
From the subsequent detailed description taken in conjunction with the accompanying claims and subjoined drawings, other objects and advantages of the present invention will become apparent to those skilled in the art.